The present invention relates to railcar truck assemblies and more specifically to an arrangement of the lands or stop surfaces between the side frames and bolster of a three-piece railcar truck assembly.
In previous railcar truck assemblies, wide laterally-extending stop surfaces or lands adjacent to the side frame wear plates and bolster friction shoe pockets have been provided to avoid rotation of the bolster about is longitudinal axis, that is, bolster rotation. Bolster antirotation stops or lugs have also been provided at the inside face of a side frame column to inhibit rotation of the bolster in the side frame about the bolster's longitudinal axis.
Railcar truck hunting is a continuous instability of a railcar wheel set wherein the truck weaves down the track in an oscillatory fashion, usually with the wheel flanges striking against the rail. A related condition known as lozenging is an unsquare condition of the side frames and bolster, and it occurs where the side frames operationally remain parallel to each other, but one side frame moves slightly ahead of the other in a cyclic fashion; this condition is also referred to as parallelogramming or warping. In truck warping, the bolster rotates about its central vertical axis, causing angular displacement of the side frame and bolster longitudinal axes from a normal relationship. Warping results in wheel misalignment with respect to the track. It is more pronounced on curved track and usually provides the opportunity for a large angle-of-attack to occur.
At the same time, the track which the railcar truck assembly traverses may change elevation. It is necessary that the side frame be able to articulate with respect to the bolster. Otherwise, as track irregularities are encountered, the side frame will tend to twist the bolster and produce substantial stresses therein. To avoid these excessive stresses, the side frame needs to be able to pitch, that is, to change its angle with respect to the bolster transverse axes.
To reduce truck warping, U.S. patent application Ser. No. 08/950,178, filed on May 2, 1997 and entitled "Improved Bolster Land Arrangement for Railcar Truck", discloses that the free travel between the mated bolster and side frame at the side frame columns may be constrained. The clearance or separation gap between the bolster lands and the side frame columns is reduced or eliminated. That patent application does not however, address the need to allow for articulation of the side frame as the track elevations vary.